The aim of this work was to optimize protein entrapment in pure poly(epsilon-caprolactone) (PCL) microparticles (MP) using the (water-in-oil)-in water solvent evaporation technique and bovine serum albumin (BSA) as drug model. Therefore, the preparative variables such as polymer solvent, protein/polymer ratio, polymer molecular weight, internal aqueous/organic phases ratio, organic/external aqueous phase ratio, and nature of the emulsifier were evaluated on microparticle characteristics such as BSA entrapment, entrapment efficiency, size and morphology. The in vitro release profiles of BSA from such MP in two different media with or without sodium dodecyl sulphate (SDS) were investigated. In optimum conditions, smooth and spherical pure PCL MP with high encapsulation efficiency (50.29 +/- 5.01%) were prepared. The release profiles of BSA in the release media were significantly different and faster in the presence of SDS. Moreover, they exhibited a relatively low burst effect after 24 h (<30%) followed by a continuous release over 28 days. Due to PCL＇s numerous desirable characteristics, such MP could be an exciting alternative for the controlled release of proteinaceous compounds.